CN114573748B

CN114573748B - Underwater adhesion anti-swelling hydrogel and flexible strain sensor

Info

Publication number: CN114573748B
Application number: CN202210345258.XA
Authority: CN
Inventors: 董晓臣; 王倩; 王嗣颖; 邵进军
Original assignee: Nanjing Tech University
Current assignee: Nanjing Tech University
Priority date: 2022-04-02
Filing date: 2022-04-02
Publication date: 2022-11-01
Anticipated expiration: 2042-04-02
Also published as: CN114573748A

Abstract

The invention discloses an underwater adhesion anti-swelling hydrogel, which is prepared by stirring alkyl acrylate, a surfactant and sodium chloride in water until the mixture is clear to obtain a precursor A, dropwise adding a ferric trichloride solution into a mixed solution of dimethylaminoethyl methacrylate, 2-hydroxyethyl acrylate and a chemical cross-linking agent, dispersing the mixture uniformly by ultrasonic to obtain a precursor B, mixing the precursor A without bubbles with the precursor B, and adopting a one-step gelling method under the action of an initiator to obtain the underwater adhesion and anti-swelling hydrogel. According to the invention, the molecular bridge relation between the gel and a target interface under water is realized through the synergy of electrostatic interaction, metal coordination and hydrophobic association, so that adhesion is realized, and the water repellency of the surface of the gel is improved by introducing a hydrophobic group, so that the stability of the gel under water is improved. The invention also discloses an underwater adhesion anti-swelling hydrogel flexible strain sensor which is formed by installing electrodes on the underwater adhesion anti-swelling hydrogel.

Description

Underwater adhesion anti-swelling hydrogel and flexible strain sensor

Technical Field

The invention relates to a preparation method of an underwater adhesion swelling-resistant hydrogel, a flexible strain sensor prepared based on the underwater adhesion swelling-resistant hydrogel, and application of the flexible strain sensor in detection of underwater adhesion, underwater swelling resistance, tensile strain and external force frequency, in particular to application in a plurality of fields of preparation of underwater real-time health monitoring equipment, underwater flexible robots, electronic skins, tensile strain detection equipment and the like.

Background

In recent years, flexible electronic devices have been completely open in the fields of information, energy, medical treatment, national defense and the like due to the characteristics of unique ductility, high efficiency, low cost manufacturing process and the like. In order to better adhere to the skin and improve the comfort during use, the electronic skin simulating various functions of the skin is developed rapidly in recent years, inspired by the skin of human beings. The hydrogel is a three-dimensional network structure gel, the aggregation state of the hydrogel is between solid and liquid, and the hydrogel has the characteristics of high hydrophilicity, strong adhesion, self-healing, good biocompatibility and the like, and is one of the selectable materials of the flexible sensor. In the preparation process of the hydrogel, along with the construction of a macromolecular crosslinking network, the swelling property and the water content of the hydrogel are determined. The hydrogel has attractive characteristics of high water content, high deformability, structural similarity with biological tissues, potential functional application and the like, and has wide application prospects in the fields of biological materials, tissue engineering, biosensors and the like. The multifunctional hydrogel integrating bionic and sensing functions also has the opportunity of being applied to the field of implantable electronic devices.

However, with the diversification of human motion, in order to meet the applicability of flexible wearable devices in various environments, higher requirements are put on gel-based flexible strain sensing materials. When people use flexible wearing equipment underwater or in a high-humidity environment, the underwater stability of the material becomes a key of the technology, but most of the traditional hydrogel absorbs water and swells in water due to the strong hydration effect underwater, the mechanical property is poor, the adhesion is reduced, the conformal effect is poor, and the development of the application field of the hydrogel underwater is seriously hindered.

Disclosure of Invention

The invention aims to overcome the defects that a hydrogel strain sensor generally has poor adhesion, poor conformal effect, water absorption swelling, reduced mechanical property and the like in an underwater environment, provides a one-step gel method for preparing hydrogel with low cost, underwater adhesion and swelling resistance, and prepares a flexible strain sensor based on the hydrogel.

The purpose of the invention is realized by the following technical scheme:

an underwater adhesion anti-swelling hydrogel is prepared by taking alkyl acrylate, dimethylaminoethyl methacrylate and 2-hydroxyethyl acrylate as raw materials, stirring the alkyl acrylate, a surfactant and sodium chloride in water until the mixture is clear to obtain a precursor A, dropwise adding a water-soluble iron salt solution into a mixed solution of the dimethylaminoethyl methacrylate, the 2-hydroxyethyl acrylate and a chemical cross-linking agent, performing ultrasonic dispersion uniformly to obtain a precursor B, mixing the precursor A without bubbles with the precursor B, and performing a one-step gel method under the action of an initiator to obtain the underwater adhesion and anti-swelling hydrogel.

Another object of the present invention is to provide a method for preparing an underwater adhesion swelling-resistant hydrogel, comprising the steps of:

fully stirring alkyl acrylate, a surfactant and sodium chloride in water at the temperature of 30-60 ℃ until the mixture is clear to obtain a precursor A; the sodium chloride is used as a cosolvent of the surfactant, meanwhile, the alkyl acrylate is more fully dissolved in water at a higher temperature, both the alkyl acrylate and the surfactant contain hydrophobic long chains, and hydrophobic parts of the alkyl acrylate and the surfactant form micelles through hydrophobic association, so that the swelling resistance of the hydrogel is enhanced;

dropwise adding a water-soluble iron salt solution into a mixed solution of dimethylaminoethyl methacrylate, 2-hydroxyethyl acrylate and a chemical cross-linking agent, uniformly stirring and ultrasonically dispersing to obtain a solution, thereby obtaining a precursor B; floccule is generated in the adding process, and the floccule is dissolved by combining ultrasonic;

removing bubbles in the precursor A in vacuum, mixing the precursor A with the precursor B, adding an initiator solution, performing ultrasonic dispersion at room temperature, and standing to obtain the underwater adhesive swelling-resistant hydrogel; micelles in the mixed solution of the precursor A and the precursor B are broken up by ultrasound, alkyl acrylate and acrylic acid-2-hydroxyethyl ester monomers are rapidly polymerized due to the fact that tertiary amino groups in dimethylaminoethyl methacrylate and persulfate generate a large number of free radicals to form a hydrogel network, and iron ions and the tertiary amino groups form a metal coordination and hydrophobic association synergistic effect to improve the stretchability, surface hydrophobicity and adhesiveness of the gel;

and (4) cleaning the hydrogel, and drying the surface.

In the step (1), the mass ratio of the sodium chloride to the surfactant is 1.

The mass ratio of the sodium chloride to the alkyl acrylate is 10.

The mass ratio of the water to the sodium chloride is 10.

The alkyl acrylate is one of octadecyl acrylate, tetradecyl acrylate and dodecyl acrylate.

The surfactant is one of sodium dodecyl benzene sulfonate and sodium dodecyl sulfate.

In the step (2), the molar ratio of the water-soluble iron salt to dimethylaminoethyl methacrylate is 1.

The concentration of the water-soluble iron salt solution is 0.0001-0.003 mol/mL.

The water-soluble ferric salt is one of ferric chloride, ferric sulfate and ferric nitrate.

The molar ratio of the dimethylaminoethyl methacrylate to the 2-hydroxyethyl acrylate is 1.

The molar ratio of the dimethylaminoethyl methacrylate to the chemical crosslinking agent is 200-400.

The chemical cross-linking agent is one of glyoxal, diphenylmethane diisocyanate, methylene bisacrylamide and acyl chloride.

In the step (3), the precursor A and the precursor B are mixed according to the mass ratio of 1.

The molar ratio of the initiator to the dimethylaminoethyl methacrylate is 1.

The concentration of the initiator solution is 0.0002-0.002 mol/mL.

The initiator is one of ammonium persulfate and potassium persulfate.

The ultrasonic power is 10-100W.

The water adopted by the invention is deionized water.

The invention also aims to provide an underwater adhesion anti-swelling hydrogel flexible strain sensor, which is formed by drying the surface of the hydrogel and then installing electrodes.

The underwater adhesion swelling-resistant hydrogel flexible strain sensor is low in cost, simple in preparation process, and has the advantages of stretchability, underwater adhesion, swelling resistance, good durability, high sensitivity, good repeatability and the like, the application of a flexible wearable device in practice can be widened, and the sensor is widely applied to the fields of electronic skin, underwater intelligent robots, underwater motion detection and the like.

The invention also aims to provide application of the underwater adhesion anti-swelling hydrogel flexible strain sensor in preparation of electronic skin, underwater real-time health monitoring equipment, underwater flexible intelligent robots and tensile strain detection equipment.

The invention has the beneficial effects that:

aiming at the problems of poor underwater adhesion, poor conformality and reduced mechanical properties caused by underwater swelling commonly existing in flexible strain sensors, the invention introduces the hydrophobic micelle, realizes the molecular bridge connection between the gel and a target interface underwater through the electrostatic hydrophobic association effect, realizes adhesion, introduces the hydrophobic group through the hydrophobic modification strategy, improves the water repellency of the surface of the gel, further improves the stability of the gel underwater, and constructs the multifunctional flexible strain sensor aiming at the detection of underwater human motion.

Drawings

FIG. 1 is a time-swelling ratio curve for different hydrogels.

FIG. 2 shows the adhesion test of the hydrogel of example 1 in air and water.

Figure 3 is a stress-strain curve of different hydrogels under water.

FIG. 4 is the sensitivity factor of the flexible strain sensor of example 1 to stretching under water.

Fig. 5 is the frequency dependence of the flexible strain sensor of example 1 under water.

FIG. 6 is the response time of the flexible strain sensor of example 1 under water.

Fig. 7 is a graph of the electromechanical responsiveness of the flexible strain sensor of example 1 under water.

Fig. 8 is the embodiment 1 flexible strain sensor in underwater mouth motion detection.

FIG. 9 shows the detection of bending motion of fingers under water by the flexible strain sensor of embodiment 1.

FIG. 10 shows the detection of finger bending movement in air by the flexible strain sensor of example 1.

Detailed Description

The technical solution of the present invention will be further described with reference to the following embodiments.

The precursor B is prepared by adopting ultrasonic conditions of 3 seconds of work, 1 second interval and 100W of power.

Example 1

Adding 0.934g of sodium chloride, 1.0224g of octadecyl acrylate and 9g of sodium dodecyl sulfate into 20mL of deionized water, and fully stirring at 50 ℃ until the mixture is clear to obtain a precursor A;

step (2), dissolving 0.081g of ferric chloride hexahydrate in 0.5mL of deionized water to prepare a ferric chloride solution, dropwise adding the ferric chloride solution into a mixed solution of 1.046g of dimethylaminoethyl methacrylate, 0.257g of acrylic acid-2-hydroxyethyl ester and 0.003g of methylene bisacrylamide, and performing ultrasonic dispersion to obtain a precursor B;

removing bubbles in the precursor A in vacuum, taking 1mL of the precursor A (containing 0.05112g of octadecyl acrylate), mixing the precursor A with the precursor B obtained in the step (2), adding an ammonium persulfate solution (prepared by dissolving 0.05g of ammonium persulfate in 0.5mL of deionized water), performing ultrasonic treatment (with ultrasonic power of 100W) for 90s in a room-temperature environment to uniformly disperse, and standing for 1 minute to obtain the hydrogel which can be adhered under water and resists swelling;

and (4) cleaning the hydrogel obtained in the step (3), drying the surface, installing electrodes to form a flexible strain sensor, wherein the size of the sensor is as follows: the length is 20mm, the width is 5mm, and the thickness is 2mm.

The swelling curve of the hydrogel of this example over 72 hours corresponds to that of PHDO-US in FIG. 1, and it can be seen that the swelling ratio of the hydrogel is maintained below 27% throughout 72 hours (i.e., the diameter of the cylindrical sample changes).

FIG. 2 shows that the hydrogel can be tightly bonded with rubber, glass, plastic, metal and other substrates in air and water, and the bonding strength is high. A large number of hydrophobic long chains exist in a hydrogel system, the surface of the hydrogel system is hydrophobic, water can be discharged firstly when adhesion is carried out underwater, and the underwater adhesion is improved.

The stress-strain curve under water for the hydrogel of this example corresponds to FIG. 3PHDO-US. In the underwater stretching process, the stretching rate and stress of the hydrogel in the example are higher than those of the hydrogels in the comparative examples 1 and 2, so that the underwater stretchability of the flexible strain sensor is ensured.

FIG. 4 is a graph of the sensitivity factor of a flexible strain sensor under water at different elongation rates. When the tensile strain is less than 100%, the relative resistance change is proportional to the elongation, and the sensitivity factor GF is about 0.44. The reliability and the accuracy of the flexible strain sensor on the human motion test are ensured.

Fig. 5 shows the detection of the flexible strain sensor in underwater environment at different stretching frequencies, and it can be seen that the sensor has stable response to 0.320, 0.243, 0.166 and 0.085 hertz of tension, and is consistent in relative resistance change under different loading rates, and shows high reliability to various forms of mechanical deformation.

Fig. 6 shows the response time of the flexible strain sensor under water, and it can be seen that the response stretch and recovery times are 106 ms and 124 ms, respectively, ensuring its rapid response to external stimuli.

Fig. 7 is a plot of the electromechanical responsiveness of the flexible strain sensor under water, and it can be seen that the relative resistance change is synchronized with the stress, indicating that negligible electromechanical hysteresis ensures excellent reproducibility and reliability of the flexible strain sensor.

Fig. 8 illustrates the use of a flexible strain sensor for mouth movement detection. The sensor is fixed at the mouth corner to judge the opening and closing state when speaking or making facial expression, and because of the obvious difference of the muscle motion degrees of the mouth corner, the relative resistance change shows obvious difference under the opening and closing state of the mouth, thereby laying a foundation for facial control and expression recognition.

The flexible strain sensor is fixed at the knuckle, the finger bending motion detection is respectively carried out in the underwater environment and in the air, the results are respectively shown in fig. 9 and fig. 10, it can be seen that the relative resistance change of the finger under different bending degrees shows obvious difference in the underwater environment and in the air, and the finger bending motion detection method has good discrimination for the finger bending motion in various environments.

Comparative example 1

step (2), dissolving 0.081g of ferric chloride hexahydrate in 0.5mL of deionized water to prepare a ferric chloride solution, dropwise adding the ferric chloride solution into a mixed solution of 1.046g of dimethylaminoethyl methacrylate, 0.257g of acrylic acid-2-hydroxyethyl ester and 0.003g of methylene bisacrylamide, uniformly stirring and ultrasonically dispersing to obtain a solution, and marking the solution as a precursor B;

step (3), vacuumizing bubbles in the precursor A, taking 1mL of the precursor A, mixing the precursor A with the precursor B obtained in the step (2), adding an ammonium persulfate solution (prepared by dissolving 0.05g of ammonium persulfate in 0.5mL of deionized water), and standing for 1 minute to obtain hydrogel;

and (4) cleaning the hydrogel obtained in the step (3), drying the surface, and mounting an electrode to form the flexible strain sensor.

The swelling curve of the hydrogel of this comparative example over 72 hours corresponds to PHDO of FIG. 1, and the stress-strain curve of the hydrogel under water corresponds to PHDO of FIG. 3. It is shown that the hydrophobic micelles are not broken and still entangled compared with example 1, and the hydrogel surface in comparative example 1 has poor water repellency and poor swelling mechanical properties.

Comparative example 2

Dissolving 0.081g of ferric chloride hexahydrate in 0.5mL of deionized water to prepare a ferric chloride solution, dropwise adding the ferric chloride solution into a mixed solution of 1.046g of dimethylaminoethyl methacrylate, 0.257g of 2-hydroxyethyl acrylate and 0.003g of methylene bisacrylamide, uniformly stirring and ultrasonically dispersing to obtain a solution, and marking the solution as a precursor B;

step (2), adding 1mL of deionized water into the precursor B, adding an ammonium persulfate solution (prepared by dissolving 0.05g of ammonium persulfate in 0.5mL of deionized water), and standing for 1 minute to obtain a hydrogel;

and (3) cleaning the hydrogel obtained in the step (4), drying the surface, and mounting an electrode to form the flexible strain sensor.

The swelling curve of the hydrogel of this comparative example over 72 hours corresponds to FIG. 1PHD, and the stress-strain curve of the hydrogel under water corresponds to FIG. 3PHD. Compared with the embodiment 1 and the comparative example 1, the hydrogel does not contain a hydrophobic part, has no hydrophobic group, has poorer surface water-repellent effect and obviously reduces the mechanical property of easier water absorption.

Claims

1. An underwater adhesion anti-swelling hydrogel, which is characterized in that: taking alkyl acrylate, dimethylaminoethyl methacrylate and 2-hydroxyethyl acrylate as raw materials, stirring the alkyl acrylate, a surfactant and sodium chloride in water until the mixture is clear to obtain a precursor A, dropwise adding a ferric trichloride solution into a mixed solution of the dimethylaminoethyl methacrylate, the 2-hydroxyethyl acrylate and a chemical cross-linking agent, performing ultrasonic dispersion uniformly to obtain a precursor B, removing bubbles in the precursor A in vacuum, mixing the precursor A and the precursor B, adding an initiator solution, performing ultrasonic dispersion at room temperature, and standing to obtain the hydrogel which can be adhered underwater and resists swelling; wherein, the alkyl acrylate is one of octadecyl acrylate, tetradecyl acrylate and dodecyl acrylate.

2. A preparation method of underwater adhesion anti-swelling hydrogel is characterized by comprising the following steps: the method comprises the following steps:

step (1), at the temperature of 30-60 ℃, stirring alkyl acrylate, a surfactant and sodium chloride in water until the mixture is clear to obtain a precursor A; the alkyl acrylate is one of octadecyl acrylate, tetradecyl acrylate and dodecyl acrylate;

dropwise adding a water-soluble iron salt solution into a mixed solution of dimethylaminoethyl methacrylate, 2-hydroxyethyl acrylate and a chemical cross-linking agent, and uniformly dispersing by ultrasonic to obtain a precursor B;

removing bubbles in the precursor A in vacuum, mixing the precursor A with the precursor B, adding an initiator solution, performing ultrasonic dispersion at room temperature, and standing to obtain the underwater adhesive swelling-resistant hydrogel;

and (4) cleaning the hydrogel, and drying the surface.

3. The method of preparing an underwater adhesion antiswelling hydrogel according to claim 2, wherein: in the step (1), the mass ratio of the sodium chloride to the surfactant is 1; the mass ratio of the sodium chloride to the alkyl acrylate is 10-6; the mass ratio of the water to the sodium chloride is 10.

4. The method of preparing an underwater adhesion anti-swelling hydrogel according to claim 2, wherein: the surfactant is one of sodium dodecyl benzene sulfonate and sodium dodecyl sulfate.

5. The method of preparing an underwater adhesion anti-swelling hydrogel according to claim 2, wherein: in the step (2), the molar ratio of the water-soluble ferric salt to the dimethylaminoethyl methacrylate is 1; the molar ratio of the dimethylamino ethyl methacrylate to the 2-hydroxyethyl acrylate is 1; the molar ratio of the dimethylaminoethyl methacrylate to the chemical crosslinking agent is 200-400.

6. The method of preparing an underwater adhesion antiswelling hydrogel according to claim 5, wherein: in the step (2), the molar ratio of the water-soluble ferric salt to the dimethylaminoethyl methacrylate is (1).

7. The method of preparing an underwater adhesion anti-swelling hydrogel according to claim 2, wherein: the concentration of the water-soluble iron salt solution is 0.0001-0.003 mol/mL;

the water-soluble ferric salt is one of ferric chloride, ferric sulfate and ferric nitrate;

the chemical cross-linking agent is one of glyoxal, diphenylmethane diisocyanate and methylene bisacrylamide.

8. The method of preparing an underwater adhesion antiswelling hydrogel according to claim 2, wherein: in the step (3), mixing the precursor A and the precursor B according to the mass ratio of alkyl acrylate to dimethylaminoethyl methacrylate of 1;

the molar ratio of the initiator to the dimethylaminoethyl methacrylate is 1;

the concentration of the initiator solution is 0.0002-0.002 mol/mL;

the initiator is one of ammonium persulfate and potassium persulfate.

9. The method of preparing an underwater adhesion antiswelling hydrogel according to claim 2, wherein: in the step (3), the ultrasonic power is 10-100W.

10. An underwater adhesion anti-swelling hydrogel flexible strain sensor is characterized in that: the flexible strain sensor is composed of the underwater adhesion anti-swelling hydrogel mounting electrode disclosed by claim 1.

11. The application of the underwater adhesion anti-swelling hydrogel flexible strain sensor of claim 10 in preparation of electronic skin, underwater real-time health monitoring equipment, underwater flexible intelligent robots and tensile strain detection equipment.